This invention relates to fuzes and more particularly to a fuze for an explosive apparatus that is protected against premature detonation until it reaches the intended target. A prior structure related to subject invention is described in U.S. Pat. No. 3,726,228 filed Nov. 23, 1970 and issued on Apr. 10, 1973. More specifically the Density Integrating Fuze Head described in the reference patent provided cross-bars as a protective shield to prevent premature detonation. The cross-bars were used in the fuze head as a mechanical barrier which allowed retaining the sensitivity of the detonator yet exposing the shell to various interferences before its impact with the ground. This barrier device including the relief vents has been particularly well adapted in actual use associated with military fuzes in a tropical environment.
The prior structure, however, as disclosed in the referenced patent has several drawbacks in that under certain situations various objects are able to by-pass the cross-bars and impact directly on the detonator causing the shell to prematurely explode. For example, the cross-bars cover less than 20 percent of the surface of the detonator permitting the detonator to be exposed to direct impact. Furthermore, the cross-bars are capable of accumulating water from raindrops and when the volume could not be retained, the water would move directly upon the detonator with a greater mass causing the shell to explode. In addition under the action of an impact force produced by leaves, limbs and thin branches a cross-bar is subject to bending and probably dislocation. In fact the resistance or stiffness of a cross-bar to bending is substantially less than the resistance of a solid protective piece resting at the base since it is susceptible only to compression. When under the action of an impact force a cross-bar is bent towards the closing disc to a deflection equal to its diameter, then the cross-bar slips out from the cross-bar holder wall and offers no more resistance against subsequent impact. These problems have prompted a re-evaluation for additional protection of the detonator requiring a closer and more critical analysis of the geometrical and kinematical parameters.
The muzzle velocity of a round is 2700 feet per second and the spin rate is 285 revolutions per second; therefore a raindrop needs only 23 microseconds to travel the length of the cylindrical frame. During the time it takes the raindrop to travel the length of the cavity, the shell rotates an angle of 2.3.degree.. This ratio of travel distance to rotation angle means that there is a definite possibility for a raindrop, snowflake or other matter, to travel the cavity length straight and undisturbed and eventually impact directly on the detonator without striking the cross-bars.
As can readily be seen, it is highly desirable that the detonator be effectively covered by a barrier. This would prevent small objects from moving directly and in an axial path gaining acceleration and impinging on the detonator triggering the fuze. An effective barrier would prevent axially moving light objects such as raindrops or leaf fragments from directly impacting the detonator while retaining the sensitivity of the detonator. A barrier would reduce considerably the probability of premature detonation since incoming material would be decelerated from the recess entrance to the bottom end of the cavity.
In the prior structure, the barrier means consisted of three cross-bars placed in a cavity in front of the detonator at equal parallel intervals perpendicular to the axis of the shell. This resulted in a partial covering of the detonator particularly at its inner perimeter, leaving the outer perimeter exposed.